/*
 * Copyright 2002-2011 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.remoting.httpinvoker;

import org.apache.commons.httpclient.Header;
import org.apache.commons.httpclient.HttpClient;
import org.apache.commons.httpclient.HttpException;
import org.apache.commons.httpclient.MultiThreadedHttpConnectionManager;
import org.apache.commons.httpclient.methods.ByteArrayRequestEntity;
import org.apache.commons.httpclient.methods.PostMethod;
import org.springframework.context.i18n.LocaleContext;
import org.springframework.context.i18n.LocaleContextHolder;
import org.springframework.remoting.support.RemoteInvocationResult;
import org.springframework.util.Assert;
import org.springframework.util.StringUtils;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.zip.GZIPInputStream;

/**
 * {@link HttpInvokerRequestExecutor} implementation that uses
 * <a href="http://jakarta.apache.org/commons/httpclient">Jakarta Commons HttpClient</a>
 * to execute POST requests. Requires Commons HttpClient 3.0 or higher.
 *
 * <p>Allows to use a pre-configured {@link org.apache.commons.httpclient.HttpClient}
 * instance, potentially with authentication, HTTP connection pooling, etc.
 * Also designed for easy subclassing, providing specific template methods.
 *
 * @author Juergen Hoeller
 * @author Mark Fisher
 * @see SimpleHttpInvokerRequestExecutor
 * @since 1.1
 */
public class CommonsHttpInvokerRequestExecutor extends AbstractHttpInvokerRequestExecutor {

    /**
     * Default timeout value if no HttpClient is explicitly provided.
     */
    private static final int DEFAULT_READ_TIMEOUT_MILLISECONDS = (60 * 1000);

    private HttpClient httpClient;


    /**
     * Create a new CommonsHttpInvokerRequestExecutor with a default
     * HttpClient that uses a default MultiThreadedHttpConnectionManager.
     * Sets the socket read timeout to {@link #DEFAULT_READ_TIMEOUT_MILLISECONDS}.
     *
     * @see org.apache.commons.httpclient.HttpClient
     * @see org.apache.commons.httpclient.MultiThreadedHttpConnectionManager
     */
    public CommonsHttpInvokerRequestExecutor() {
        this.httpClient = new HttpClient(new MultiThreadedHttpConnectionManager());
        setReadTimeout(DEFAULT_READ_TIMEOUT_MILLISECONDS);
    }

    /**
     * Create a new CommonsHttpInvokerRequestExecutor with the given
     * HttpClient instance. The socket read timeout of the provided
     * HttpClient will not be changed.
     *
     * @param httpClient the HttpClient instance to use for this request executor
     */
    public CommonsHttpInvokerRequestExecutor(HttpClient httpClient) {
        this.httpClient = httpClient;
    }


    /**
     * Set the HttpClient instance to use for this request executor.
     */
    public void setHttpClient(HttpClient httpClient) {
        this.httpClient = httpClient;
    }

    /**
     * Return the HttpClient instance that this request executor uses.
     */
    public HttpClient getHttpClient() {
        return this.httpClient;
    }

    /**
     * Set the connection timeout for the underlying HttpClient.
     * A timeout value of 0 specifies an infinite timeout.
     *
     * @param timeout the timeout value in milliseconds
     * @see org.apache.commons.httpclient.params.HttpConnectionManagerParams#setConnectionTimeout(int)
     */
    public void setConnectTimeout(int timeout) {
        Assert.isTrue(timeout >= 0, "Timeout must be a non-negative value");
        this.httpClient.getHttpConnectionManager().getParams().setConnectionTimeout(timeout);
    }

    /**
     * Set the socket read timeout for the underlying HttpClient.
     * A timeout value of 0 specifies an infinite timeout.
     *
     * @param timeout the timeout value in milliseconds
     * @see org.apache.commons.httpclient.params.HttpConnectionManagerParams#setSoTimeout(int)
     * @see #DEFAULT_READ_TIMEOUT_MILLISECONDS
     */
    public void setReadTimeout(int timeout) {
        Assert.isTrue(timeout >= 0, "Timeout must be a non-negative value");
        this.httpClient.getHttpConnectionManager().getParams().setSoTimeout(timeout);
    }


    /**
     * Execute the given request through Commons HttpClient.
     * <p>This method implements the basic processing workflow:
     * The actual work happens in this class's template methods.
     *
     * @see #createPostMethod
     * @see #setRequestBody
     * @see #executePostMethod
     * @see #validateResponse
     * @see #getResponseBody
     */
    @Override
    protected RemoteInvocationResult doExecuteRequest(
            HttpInvokerClientConfiguration config, ByteArrayOutputStream baos)
            throws IOException, ClassNotFoundException {

        PostMethod postMethod = createPostMethod(config);
        try {
            setRequestBody(config, postMethod, baos);
            executePostMethod(config, getHttpClient(), postMethod);
            validateResponse(config, postMethod);
            InputStream responseBody = getResponseBody(config, postMethod);
            return readRemoteInvocationResult(responseBody, config.getCodebaseUrl());
        } finally {
            // Need to explicitly release because it might be pooled.
            postMethod.releaseConnection();
        }
    }

    /**
     * Create a PostMethod for the given configuration.
     * <p>The default implementation creates a standard PostMethod with
     * "application/x-java-serialized-object" as "Content-Type" header.
     *
     * @param config the HTTP invoker configuration that specifies the
     *               target service
     * @return the PostMethod instance
     * @throws IOException if thrown by I/O methods
     */
    protected PostMethod createPostMethod(HttpInvokerClientConfiguration config) throws IOException {
        PostMethod postMethod = new PostMethod(config.getServiceUrl());
        LocaleContext locale = LocaleContextHolder.getLocaleContext();
        if (locale != null) {
            postMethod.addRequestHeader(HTTP_HEADER_ACCEPT_LANGUAGE, StringUtils.toLanguageTag(locale.getLocale()));
        }
        if (isAcceptGzipEncoding()) {
            postMethod.addRequestHeader(HTTP_HEADER_ACCEPT_ENCODING, ENCODING_GZIP);
        }
        return postMethod;
    }

    /**
     * Set the given serialized remote invocation as request body.
     * <p>The default implementation simply sets the serialized invocation as the
     * PostMethod's request body. This can be overridden, for example, to write a
     * specific encoding and to potentially set appropriate HTTP request headers.
     *
     * @param config     the HTTP invoker configuration that specifies the target service
     * @param postMethod the PostMethod to set the request body on
     * @param baos       the ByteArrayOutputStream that contains the serialized
     *                   RemoteInvocation object
     * @throws IOException if thrown by I/O methods
     * @see org.apache.commons.httpclient.methods.PostMethod#setRequestBody(java.io.InputStream)
     * @see org.apache.commons.httpclient.methods.PostMethod#setRequestEntity
     * @see org.apache.commons.httpclient.methods.InputStreamRequestEntity
     */
    protected void setRequestBody(
            HttpInvokerClientConfiguration config, PostMethod postMethod, ByteArrayOutputStream baos)
            throws IOException {

        postMethod.setRequestEntity(new ByteArrayRequestEntity(baos.toByteArray(), getContentType()));
    }

    /**
     * Execute the given PostMethod instance.
     *
     * @param config     the HTTP invoker configuration that specifies the target service
     * @param httpClient the HttpClient to execute on
     * @param postMethod the PostMethod to execute
     * @throws IOException if thrown by I/O methods
     * @see org.apache.commons.httpclient.HttpClient#executeMethod(org.apache.commons.httpclient.HttpMethod)
     */
    protected void executePostMethod(
            HttpInvokerClientConfiguration config, HttpClient httpClient, PostMethod postMethod)
            throws IOException {

        httpClient.executeMethod(postMethod);
    }

    /**
     * Validate the given response as contained in the PostMethod object,
     * throwing an exception if it does not correspond to a successful HTTP response.
     * <p>Default implementation rejects any HTTP status code beyond 2xx, to avoid
     * parsing the response body and trying to deserialize from a corrupted stream.
     *
     * @param config     the HTTP invoker configuration that specifies the target service
     * @param postMethod the executed PostMethod to validate
     * @throws IOException if validation failed
     * @see org.apache.commons.httpclient.methods.PostMethod#getStatusCode()
     * @see org.apache.commons.httpclient.HttpException
     */
    protected void validateResponse(HttpInvokerClientConfiguration config, PostMethod postMethod)
            throws IOException {

        if (postMethod.getStatusCode() >= 300) {
            throw new HttpException(
                    "Did not receive successful HTTP response: status code = " + postMethod.getStatusCode() +
                            ", status message = [" + postMethod.getStatusText() + "]");
        }
    }

    /**
     * Extract the response body from the given executed remote invocation request.
     * <p>The default implementation simply fetches the PostMethod's response body stream.
     * If the response is recognized as GZIP response, the InputStream will get wrapped
     * in a GZIPInputStream.
     *
     * @param config     the HTTP invoker configuration that specifies the target service
     * @param postMethod the PostMethod to read the response body from
     * @return an InputStream for the response body
     * @throws IOException if thrown by I/O methods
     * @see #isGzipResponse
     * @see java.util.zip.GZIPInputStream
     * @see org.apache.commons.httpclient.methods.PostMethod#getResponseBodyAsStream()
     * @see org.apache.commons.httpclient.methods.PostMethod#getResponseHeader(String)
     */
    protected InputStream getResponseBody(HttpInvokerClientConfiguration config, PostMethod postMethod)
            throws IOException {

        if (isGzipResponse(postMethod)) {
            return new GZIPInputStream(postMethod.getResponseBodyAsStream());
        } else {
            return postMethod.getResponseBodyAsStream();
        }
    }

    /**
     * Determine whether the given response indicates a GZIP response.
     * <p>The default implementation checks whether the HTTP "Content-Encoding"
     * header contains "gzip" (in any casing).
     *
     * @param postMethod the PostMethod to check
     * @return whether the given response indicates a GZIP response
     */
    protected boolean isGzipResponse(PostMethod postMethod) {
        Header encodingHeader = postMethod.getResponseHeader(HTTP_HEADER_CONTENT_ENCODING);
        return (encodingHeader != null && encodingHeader.getValue() != null &&
                encodingHeader.getValue().toLowerCase().contains(ENCODING_GZIP));
    }

}
